1. Field of the Invention
The present application relates to a nitride semiconductor structure and a method for manufacturing the same.
2. Description of Related Art
In recent years, light emitting diodes (LEDs) and laser diodes (LDs) are now prevailing in commercial use. For instance, a mixture of blue and yellow phosphor powder made of gallium nitride (GaN) is capable of generating white light, which leads to high luminance and substantially low power consumption in comparison with a conventional light bulb. In addition, the LED has a lifetime of more than tens of thousand hours, longer than that of the conventional light bulb.
In the process of manufacturing a GaN semiconductor light-emitting element, due to difference in lattice constants and thermal expansion coefficients between a GaN semiconductor layer and an epitaxy substrate, the GaN semiconductor easily encounters the problems of threading dislocation and thermal stresses during an epitaxy process, which deteriorates luminance efficiency of the light-emitting element.
According to the related art, a method of separating the GaN semiconductor layer from the epitaxy substrate includes applying an irradiating method whereby laser beams pass through a substrate and illuminate an interlayer between the substrate and the GaN semiconductor layer. Thus, the GaN semiconductor layer and the epitaxy substrate are separated. Moreover, a wet etching method can also be performed to directly remove a barrier structure between the substrate and the GaN semiconductor layer so as to weaken a connection structure therebetween and to further separate the GaN semiconductor layer from the epitaxy substrate. In addition, a vapor phase etching process can be performed at a high temperature to directly remove the interlayer between the GaN semiconductor layer and the epitaxy substrate. Thus, the GaN semiconductor layer and the epitaxy substrate are separated.
For instance, in U.S. Pat. No. 6,582,986, a method of forming a GaN semiconductor layer by pendeo-epitaxy is disclosed. This method is adapted for being applied to materials apt to be etched, e.g., a carbon silicon substrate, while stresses are prone to be concentrated at a buffer layer which is located between the epitaxy substrate and the GaN semiconductor layer and serves as a seed.
On the other hand, in PCT publication no. WO2007/107757, a method of adjusting epitaxy parameters is provided. As indicated in FIG. 1, an epitaxy process is performed directly on an epitaxy substrate 100 to form a GaN nanocolumn 102 on a nitride layer 101. Next, by using the GaN nanocolumn 102 as a seed, an epitaxial lateral over growth (ELOG) process is performed to form a GaN semiconductor thick film 104. A cooling process is then carried out to crack an interface between the GaN semiconductor layer 104 and the epitaxy substrate 100. Thereafter, a mechanical force is applied to separate a GaN thick film from the GaN semiconductor layer 104 and the epitaxy substrate 100.